This invention relates to printing presses, and, more particularly, to a quick change system for a press such as a flexographic press.
The multicolor flexographic printing process requires the use of components specific to each job. These components consist of the following:
1. plate cylinders, the diameter of which corresponds to the repeat dimensions of the image being printed; PA1 2. anilox rolls, whose cell variables depend upon the characteristics of the ink and image being printed; PA1 3. the inks and their containers. PA1 1. Manual hoist systems. This type of system utilizes I-beams running parallel to the center line of the press. Chain fall hoists, which travel along the I-beams, are equipped with adapters which attach to the journals of the plate cylinders and anilox rolls. With the adapters in place, the components can be lifted from the color deck of the press and placed in a roll cart. Likewise, new (made ready) components are transported back to the color deck. PA1 2. Synchronized hoist systems. This type of system is similar in function to a manual hoist system except for the synchronized motion of the chain falls. It is easier to use and can provide a quicker changeover than the manual type system. PA1 3. Robotic systems. A typical system travels across the press in the same fashion as the hoist systems. A cylinder or roll location in the press, location in the cart, and path between the two are programmed. A robotic system can be quicker and safer to use than the hoist type systems. PA1 1. Changeover operations must be robotic, rather than operator paced, in order to guarantee changeover time requirements. When attempting to accomplish 15 minute changeovers, the variable human factors become too great. Although not directly related to changeover, robotics can also provide for a safer working environment and less change of component damage during changeover. Programmed exchange moves need to be entered into the robot controller prior to the changeover process. PA1 2. Clean-up of any components cannot be done on the press. This is a time-consuming task which holds up all tasks following it. PA1 3. A new design must be versatile. It must provide for a quick complete changeover, yet still be able to provide partial (one component at a time) exchanges when necessary. PA1 4. The design must maintain current print quality in the finished product. PA1 1. Color Deck Carriage: A color deck carriage consists of a set of frames housing the anilox roll and the support structure for the ink handling system for a single color deck. The ink handling system will include the doctor holder, ink container, pump, viscosity control system, drip containment pan, and required hoses and piping. The anilox roll is removably positioned in the carriage frame by a set of journal caps. This carriage is independent of the press itself. It provides a totally integrated ink delivery system. It is transported to and from the color deck by a robotic system. It could also be transported by other more manual means such as a hoist system. PA1 2. Staging Structure: Each printing deck requires two color deck carriages. One is staged within the press during a run. The second is located on a staging structure in a make-ready state. A staging area, facilitated by the staging structure, provides the means to prepare the carriage for the next press run. All clean-up, roll exchanges, and next job set-up are accomplished while the press is running a job. This allows internal changeover tasks to be converted to external tasks as changeover process study requires. PA1 3. Robotic System: The color deck carriage can be transported in a number of ways. The most efficient method would involve the use of a robotic system. The robot to be described will complement the function of the previously described color deck carriage. It is also versatile enough to allow for partial exchanges which would not necessarily involve the carriage. It improves changeover tasks over standard prior art robots by transporting all of the components for an entire deck, thereby eliminating the need for multiple exchanges during the changeover time. The robot is capable of motion in three directions or axes: PA1 1. motion between the press and the staging structure; PA1 2. motion into and out of the press section or into and out of the staging structure, essentially a horizontal motion; PA1 3. motion in the vertical axis.
All of these components need to be exchangeable. There may be situations where an unfavorable anilox roll will be changed during a run. A plate cylinder change may be the only component change if the same ink is going to be used on the next job. Perhaps the ink mixture is not producing the desired print quality and needs to be replaced. A common changeover will require all components to be exchanged in preparation for a completely new print run.
A typical wide web central impression printing press will be provided with some means of operator assistance for component exchange. Operator assistance is required since the plate rolls can weigh up to 800 pounds or more and the anilox rolls can weight in the range of 500 pounds. Operator assistance includes:
Hoist and robotic systems have proved useful in daily pressroom operations. Still, problems exist. Those systems are not capable of changing doctor holders or ink containers. For example, U.S. Pat. No. 5,010,813 describes a robot that can replace a single cylinder. Furthermore, plate and anilox rolls need to be cleaned before they can be removed from the press. Changeover on this size of machine cannot be obtained in a quick enough fashion with the common hoist or robotic system.
In the past a typical press run was longer than it is today. A six-hour run was followed by a two-hour changeover. This example produced a 25 percent downtime. Shorter print runs are common today. A more typical run of two hours is still followed by a two-hour changeover. Thus, a 50 percent downtime factor results. Downtime does not produce revenue.
Other printing machines such as a narrow web press and gravure press condense the changeover time by separate methods. Both types of machines have design compromises. The narrow web industry has adopted the philosophy of using cartridges that contain the inking unit and print cylinder. However, these cartridges are small (under 100 pounds and maximum width of 20 inches) and can be handled by the operator, unlike the wide web application. For example, U.S. Pat. No. 5,060,569 describes a cartridge that can be slid into position on a pair of rails by the operator. Furthermore, the cartridge in that patent is located in the press by using the frame of the cartridge instead of the printing cylinder.
A gravure press also incorporates a cart system to decrease the changeover time. A gravure cart is wheeled into place and is always on the floor. The cart is larger, but the gravure application has the advantage of space because the process does not require printing on a central impression drum. A gravure press like most narrow web presses uses an in-line configuration that does not print quality (color-to-color register within 0.003 inch) images on extensible webs. These cartridges in both cases also have the problem of not being able to replace the print cylinder without replacing the cartridges